Histone acetyltransferase (HAT) activity of p300 modulates human T lymphotropic virus type 1 p30{sup II}-mediated repression of LTR transcriptional activity

Human T-lymphotropic virus type-1 (HTLV-1) is a deltaretrovirus that causes adult T cell leukemia/lymphoma, and is implicated in a variety of lymphocyte-mediated inflammatory disorders. HTLV-1 provirus has regulatory and accessory genes in four pX open reading frames. HTLV-1 pX ORF-II encodes two proteins, p13{sup II} and p30{sup II}, which are incompletely defined in virus replication or pathogenesis. We have demonstrated that pX ORF-II mutations block virus replication in vivo and that ORF-II encoded p30{sup II}, a nuclear-localizing protein that binds with CREB-binding protein (CBP)/p300, represses CREB and Tax responsive element (TRE)-mediated transcription. Herein, we have identified p30{sup II} motifs important for p300 binding and in regulating TRE-mediated transcription in the absence and presence of HTLV-1 provirus. Within amino acids 100-179 of p30{sup II}, a region important for repression of LTR-mediated transcription, we identified a single lysine residue at amino acid 106 (K3) that significantly modulates the ability of p30{sup II} to repress TRE-mediated transcription. Exogenous p300, in a dose-responsive manner, reverses p30{sup II}-dependent repression of TRE-mediated transcription, in the absence or presence of the provirus, In contrast to wild type p300, p300 HAT mutants (defective in histone acetyltransferase activity) only partially rescued p30{sup II}-mediated LTR repression. Deacetylation by histone deacetylase-1 (HDAC-1) enhanced p30{sup II}-mediated LTR repression, while inhibition of deacetylation by trichostatin A decreases p30{sup II}-mediated LTR repression. Collectively, our data indicate that HTLV-1 p30{sup II} modulates viral gene expression in a cooperative manner with p300-mediated acetylation.